FAILED: patch "[PATCH] KVM: arm64: vgic-its: Reject restored DTE with out-of-range" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 9ce754ed8e7ab4e3999767ce1505f85c449ccb07
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026052854-saga-absentee-40e2@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 9ce754ed8e7ab4e3999767ce1505f85c449ccb07 Mon Sep 17 00:00:00 2001
From: Michael Bommarito <[email protected]>
Date: Tue, 19 May 2026 09:25:19 -0400
Subject: [PATCH] KVM: arm64: vgic-its: Reject restored DTE with out-of-range
num_eventid_bits

Userspace can restore an ITS Device Table Entry whose Size field encodes more EventID bits than the virtual ITS supports. The live MAPD path rejects that state, but vgic_its_restore_dte() accepts it and stores the out-of-range value in dev->num_eventid_bits.

Reject restored DTEs with num_eventid_bits > VITS_TYPER_IDBITS before allocating the device. This mirrors the MAPD check and prevents the restored state from reaching vgic_its_restore_itt(), where the unchecked value can be converted into an oversized scan_its_table() range.

index 2ea9f1c7ebcd..1d7e5d560af4 100644
@@ -2307,6 +2307,10 @@ static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
 	/* dte entry is valid */
 	offset = (entry & KVM_ITS_DTE_NEXT_MASK) >> KVM_ITS_DTE_NEXT_SHIFT;
 
+	/* Mimic the MAPD behaviour and reject invalid EID bits. */
+	if (num_eventid_bits > VITS_TYPER_IDBITS)
+		return -EINVAL;
+
 	if (!vgic_its_check_id(its, baser, id, NULL))
 		return -EINVAL;